Pressure responsive initiator



A ril 14, 1964 cs. A. NODDIN ETAL PRESSURE RESPONSIVE INITIATOR Filed April 25. 1961 INVENTORS GEORGE ADELBERT NOD'DIN JAMES PERSHING SWED W- ORNEY United States Patent 3,128,704 PRESSURE RESPONSIVE INITIATOR George Adelbert Noddin, Sewell, and James Pershing Swed, Gibbstown, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., :1 corporation of Delaware Filed Apr. 25, 1961, Ser. No. 105,494 6 Claims. (Cl. 10270) The present invention relates to initiators and, more particularly, to a pressure-responsive initiator characterized by a mechanism for regulating and calibrating the firing pressure thereof.

For activities in which the detonation of explosive charges below the surface of water is desired, such as in seismic exploration, underwater signalling, echo-ranging for detection purposes, and destruction of undersea craft, the need exists for a reliable and accurate initiator responsive to the hydrostatic pressure of the water at some predetermined depth. Such an initiator obviates the need for wires leading from the surface to the charge or for timing devices to effect actuation of an initiator.

Substantial progress in fulfilling this need has been made by the art. For example, United States patent application Serial No. 64,087, filed October 21, 1960, now US. Patent 3,095,815, discloses a pressure-responsive initiator comprising a piston and an explosive charge-containing unit housed in a shell, wherein the slidably mounted piston engages a spring which allows the piston to be depressed under tension as pressure is applied to its exposed extremity. As the pressure is increased, an inhibited striker arm is disengaged to cause the explosive charge to ignite. While many prior problems are eliminated by such a device, still further advances are needed to provide 'an initiator which will detonate an explosive charge at a predetermined depth and an initiator which can be easily adjusted just prior to use to cause detonation of the unit at any given depth.

In accordance with the present invention, a novel pressure responsive initiator is provided which contains a means for adjusting the assembled initiator for actuation at any desired depth and for verifying the accuracy of adjustment wtihout the destruction of the unit. The device comprises a tubular shell open at both ends and having an axially projecting base at one end thereof; a movable piston closing one end of the tube; a flexible striker arm fastened to the inner end of the piston and curved so that the free end points toward the side wall of the tube; a striker arm arresting element contained within said shell so that it is in alignment with the free end of the striker arm; an adjustment collar mounted on said base for'movement toward either end of said shell; a compression spring mounted on the piston-receiving tubular shell and interposed between the piston and the adjustment collar; a removable explosive charge containing unit adapted to mate with the base of the piston-receiving cylinder; an anvil head formed on the inner end of explosive charge-containing unit; a percussion-sensitive composition disposed upon the anvil; and a longitudinal bore within said explosive charge containing unit adapted to contain the initiating charge. In a preferred embodiment of this invention, the explosive charge contains, sequentially downward, an ignition or deflagrating charge, a priming charge, and a base charge. In a particularly preferred embodiment of the invention, a tubular outer shell surrounds the assembled unit. This shell may have an aperture adjacent to the adjustment collar to facilitate adjustment of the assembled unit. In accordance with this invention, the free end of the striker arm is prevented from contacting the percussion-sensitive charge until downward movement of the piston effected by increasing external pressure is suflicient to overcome the tension of 3,128,704 Patented Apr. 14, 1964 the compression spring and to bend the striker arm to the degree that the free end slips off the arresting element onto the percussion sensitive charge.

In order to more fully describe the present invention, reference is made to the accompanying drawing which represents a partially sectional view of a preferred embodiment of the device of the present invention.

Referring now to the drawing in greater detail, 1 represents a protective tubular outer shell open at both ends, 2 is an adjustment aperture formed in the side of the shell and 19 is a hole for the locking pin 20. The pistonreceiving tubular shell includes tube 3 and base section 4, which is fastened thereto. Base 4 is threaded to mate with the shell 1 and with explosive charge containing unit 5. Partially within one end of the tube 3 is piston 6 containing a pair of sealing rings 7. Attached to the bottom of the piston is striker arm 8. A striker arm arresting element 9 is integral with base 4 and is in alignment with the striker arm 8. Compression spring 10 fits about the tube 3 and rests on adjustment collar 11 which is used to regulate the tension on spring 10. The adjustment collar 11 contains evenly spaced tool holes 12. An explosive charge-containing unit 5 is secured within and closes the open end of the shell 1. The longitudinal bore 14 of the unit 5 houses an ignition charge 15 and a second shell 16 which contains a priming charge 17 and a base charge 18. An anvil head 22 having an annular aperture therethrough is seated within the longitudinal bore 14 at the inner extremity thereof, and a percussionsensitive explosive composition 13 is mounted on the inner extremity of the unit 5 so that it is in alignment with the striker arm 8 when the piston 6 is in the depressed position. Sealing rings 21 surround the unit 5. Sealing ring 23 surrounds the flange of piston 6.

In operation, the pin 20 is removed and the assembly dropped in the body of water. The increasing hydrostatic pressure encountered with increasing depth forces piston 6 inwardly in tubular shell 3 against the pressure of the air entrapped inside and against the resistance of compression spring 10. As the inward movement continues, the end of the striker arm 8 moves suificiently to clear arrester 9, and snaps onto the percussion sensitive charge 13 which becomes ignited and sets 01f the ignition composition 15 which effects initiation of the priming and base charges 17 and 18.

The pressure at which striker arm 8 snaps oif arrester 9 depends on frictional resistance, compression of air in the tubes, the stiffness of the striker arm 8, and the tension spring 10. The effective surface area of the piston is also involved. For actuation at shallow depth, i.e., low pressure, sealing ring 23 is used and tubular shell 1 is sealed to form a watertight chamber so that the eifective area of piston 6 is represented by the area of the flanged portion. For greater depths, sealing ring 23 is omitted and entrance of water into shell 1 is permitted, making the effective area of piston 6 that of the diameter of tube 3. The tension of spring 16 is adjusted by means of collar 11 which is rotated on threaded base 4. Rotation is facilitated by tool openings 12 and, when shell 1 is present, an access aperture 2. If shell 1 is to be made watertight for shallow depth operation, aperture 2 is either omitted or sealed by a tape or similar closure.

In the device of this invention, all explosive components are contained in a unit, i.e., unit 5, which may be stored charge-containing unit similar to unit 5 containing only a percussion-sensitive composition 13 is screwed into position, pressure is applied to piston 6 equivalent to that which will act on piston 6 at the desired depth, and collar '12 is turned to decrease tension on spring 10 until the audible sound from the initiation of composition 13 indicates that striker arm 8 has snapped from arrester 9.

The aperture 2 may contain marks indicating the approximate depth at which the assembly will be actuated when a corresponding mark on the collar 10 is in alignment therewith. The accuracy of such marks can be verified by using a dummy unit 5, and measuring the pressure at which actuation occurs. Restoration of piston 6 to its original position returns the assembly to the same condition as before the test so that it will be reproducibly actuated by essentially the identical pressure.

The striker arm used in this device is attached at one end to the piston, the free end is pointed toward the side wall and is aligned with the arresting element. Since this arm does not rest on the arresting element, no tension is exerted on the arm absent hydrostatic pressure on the assembly. The absence of tension makes the device very reliable because the resistance to bending of the striker arm does not change. This absence of tension also makes the loaded assembly safer to handle. When pressure is exerted to depress the piston within the shell, the end of the striker arm is met and held by the arresting element until the critical point is reached, whereupon the striker arm snaps from the arresting element with ample striking energy to meet and set off the percussion-sensitive charge.

The anvil and arresting device may be of any design, straight or irregular, wherein the arresting device holds the striker arm until the critical pressure is reached and wherein the striker arm can snap off the arresting device down onto the percussion-sensitive mixture. The arresting device may be annular or occupy only a portion of the inner periphery of the shell.

As an additional safety factor, and also to insure alignment of the striker arm within the arrester, the piston preferably is locked in the extended position by a locking pin. Removal of the pin is all that is required to arm the assembly.

The striker arm is preferably fabricated of a spring steel, although it may be of any material of suflicient resiliency to snap onto the percussion-sensitive material after it is moved past its contact with the arrester.

The materials of the shell, anvil, or compression spring are not critical as long as these components are waterresistant and possess sufiicient structural strength to withstand the pressure at the predetermined depth. Any conventional ignition, priming, and percussion-sensitive composition can be used in the device. As the base charge may be used either a detonating explosive composition or a defiagrating explosive composition, depending on whether a detonator or squib action is desired.

The following example is further illustrative of the present invention, but it is to be understood that the invention is not limited thereto.

Example I An initiator as illustrated in FIGURE 1 was constructed. The tubular outer shell of aluminum had an inner diameter of 0.875 inch, an outer diameter of one inch, and a length of 3.125 inches. The tubular shell of aluminum was 1.562 inches long and had an inner diameter of 0.5 inch and a wall thickness of 0.010 inch, the tubular shell Was mounted on a base of 1.000 inch outer diameter and 0.500 inch inner diameter at its lower part through a threaded section containing 20* equidistant machined threads and having an inner diameter of 0.375 inch and an outer diameter of 0.5 inch. The locking pin consisted of a length of 0.059 inch diameter steel wire. The removable explosive charge containing unit was of aluminum 1.500 inch long; at the upper 1.288 inch section of the anvil the piece had an outer diameter of 0.373 inch and an inner diameter of A3 inch, while at the threaded lower 0.212 inch the outer diameter was 0.500 inch and the inner diameter was 0.246 inch. The movable piston was also of aluminum with a length of 1.000 inch. The striker arm was 0.020 inch diameter spring steel having a length of 0.688 inch, flat on top with a 0.093 inch radius curve, followed by a straight length of a 0.125 inch radius curve and terminating in a straight length 0.129 inch long, the tip of which was aligned 0.031 inch above the arresting element. The compression spring was a 180 pound/ inch compression spring, and the threaded adjustment collar was of brass and was 1.5 inch long, 0.89 inch in diameter, and provided with six holes spaced at 60 angles about the circumference of the lower part of the collar. .The percussion-sensitive mixture used was an adhesive-backed toy cap. The assembled unit was fired in water under nitrogen pressure by increasing the pressure incrementally until the toy cap was initiated. After each test, the unit was retrieved, the toy cap replaced and the reloaded unit again fired. Two readings were made at each of ten different settings as shown in the table.

Firing lressure (p.s.1.ga.) Collar Setting (Turns from Bottom) 1st Shot 2nd Shot Example II The explosive charge containing unit of the detonator prepared in Example I was replaced by a unit loaded as follows: An ignition composition comprising 0.5 grain of a mixture of 50 ground smokeless powder, 25% of the lead salt of dinitro-orthocresol and 25 potassium chlorate was placed in the hole of the anvil and a length of conventional deflagrating fuse was placed in the container abutting the ignition mixture. A detonator containing in sequence in a thin Walled aluminum tube, 0.7

grain of an ignition mixture comprising a 98.75/0.75/0.5 mixture of lead .styphnate/graphite/calcium stearate, 2 grains of lead azide as a priming composition, and 3 grains PETN as a base charge was immediately below and in propagating relationship to the fuse. A toy cap was again used as the percussion-sensitive charge. The collar was set at four full turns. When the unit was submerged in water under nitrogen pressure increased incrementally, the initiator was actuated at 214 pounds per square inch.

Although the present invention has been described in detail in the foregoing, it will be apparent to those skilled in the art that many variations in design are possible without departure from the scope of the invention. It is intended, therefore, to be limited only by the following claims.

We claim:

1. A hydrostatic pressure-responsive initiator comprising a tubular shell open at both ends and having an axially projecting base at one extremity thereof, a piston slidably mounted within and closing the end opposite the containing unit secured within said base and closing the open extremity of the shell, a percussion sensitive ignition composition mounted on the contained inner extremity of the said explosive unit in striking relationship to said striker arm and a striker arm arrester extending from the side wall of the shell and between the free end of the striker arm and said ignition composition, the alignment of said free end, the striker arm arrester, and the ignition composition being such that upon gradual depression of said piston, the striker arm first engages and is compressed by the striker arm arrester and then slips oiT said arrester and snaps onto said ignition composition.

2. The device of claim 1 wherein the spring means is a coiled compression spring.

3. The device of claim 1 wherein the said initiator is enclosed in a tubular housing provided with an aperture adjacent to, and communicating with, said adjustment collar.

4. The device of claim 1 wherein the free end of the striker arm is maintained in position spaced from but closely adjacent to the striker arm arrester by a removable pin which engages the piston.

5. A hydrostatic pressure-responsive initiator comprising a cylindrical shell open at both ends and having an axially projecting base at one extremity thereof, a piston slidably mounted Within and closing the end opposite the base of said shell, said piston having a circumferential flange at its exposed extremity, a flexible, resilient striker arm fixed to the inner end of the piston and curved so that its free end extends toward the side Wall of said shell, a collar threadably mounted on said base for threaded movement toward either extremity of the shell, a spring means mounted on the shell and abutting both the said collar and the piston flange, an elongated explosive charge-containing unit removably secured within said base and closing the open extremity of the shell, said unit having a longitudinal bore adapted to contain an explosive charge, an anvil head seated within the inner extremity of said explosive unit, and a percussion sensitive ignition composition fixed on said anvil in propagating relationship to said explosive charge and in striking relationship to said striker arm and a striker arm arrester extending from the side wall of the shell and between the free end of the striker arm and said ignition composition, the alignment of said free end, the striker arm arrester, and the ignition composition being such that upon gradual depression of said piston, the striker arm first engages and is compressed by the striker arm arrester and then slips off said arrester and snaps onto said ignition composition.

6. The device of claim 5 wherein the explosive charge-containing unit contains in sequence from the percussion sensitive ignition composition to the shell extremity, a deflagrating composition, a priming charge and a base charge.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,718 Rasmussen Apr. 16, 1946 2,720,167 Hesson Oct. 11, 1955 2,763,212 McCaslin Sept. 18, 1956 2,998,770 Bernard Sept. 5, 1961 FOREIGN PATENTS 126,326 Great Britain May 15, 1919 276,745 Switzerland Nov. 1, 1951 

1. A HYDROSTATIC PRESSURE-RESPONSIVE INITIATOR COMPRISING A TUBULAR SHELL OPEN AT BOTH ENDS AND HAVING AN AXIALLY PROJECTING BASE AT ONE EXTREMITY THEREOF, A PISTON SLIDABLY MOUNTED WITHIN AND CLOSING THE END OPPOSITE THE BASE OF SAID SHELL, SAID PISTON HAVING A CIRCUMFERENTIAL FLANGE AT ITS EXPOSED EXTREMITY, A FLEXIBLE, RESILIENT STRIKER ARM FIXED TO THE INNER END OF THE PISTON AND CURVED SO THAT ITS FREE END EXTENDS TOWARD THE SIDE WALL OF SAID SHELL, A COLLAR THREADABLY MOUNTED ON SAID BASE FOR MOVEMENT TOWARD EITHER EXTREMITY OF THE SAID SHELL, A SPRING MEANS MOUNTED ON THE SHELL AND ABUTTING BOTH THE SAID COLLAR AND THE SAID PISTON FLANGE, AN EXPLOSIVE CHARGECONTAINING UNIT SECURED WITHIN SAID BASE AND CLOSING THE OPEN EXTREMITY OF THE SHELL, A PERCUSSION SENSITIVE IGNITION COMPOSITION MOUNTED ON THE CONTAINED INNER EXTREMITY OF THE SAID EXPLOSIVE UNIT IN STRIKING RELATIONSHIP TO SAID STRIKER ARM AND A STRIKER ARM ARRESTER EXTENDING FROM THE SIDE WALL OF THE SHELL AND BETWEEN THE FREE END OF THE STRIKER ARM AND SAID IGNITION COMPOSITION, THE ALIGNMENT OF SAID FREE END, THE STRIKER ARM ARRESTER, AND THE IGNITION COMPOSITION BEING SUCH THAT UPON GRADUAL DEPRESSION OF SAID PISTON, THE STRIKER ARM FIRST ENGAGES AND IS COMPRESSED BY THE STRIKER ARM ARRESTER AND THEN SLIPS OFF SAID ARRESTER AND SNAPS ONTO SAID IGNITION COMPOSITION. 